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y2k silver'sight, hch1 5spd, snow tires
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Discussion Starter · #101 ·
earlier on in this thread i mentioned putting batteries in a cooler. maybe i'll turn my pickup truck into a hybrid and try it on that someday. speaking of hybrid pickup's, the hybrid tundra is like a knock off of the g1 insight. its a parallel hybrid with nimh cells. key difference is the electric motor has an electric clutch that disconnects from the ice. the concept is to improve economy by downsizing engine and having assist for accel, eerie similarities of form fit and function
 

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Revisiting this graphic for EHW5* modules (which are not the 5AhG3 modules used with LiBCM):
Rectangle Slope Font Line Plot


Looks like EHW5* modules can handle some regen at least down to -10 degC, proportional to SoC. The 5AhG3 modules are different from EHW5, but at least in this case a 48S pack would have 12 kg of cells, which would mean you could regen up to 6 kW at 20% SoC in -10 degC weather. Obviously I need to find this same graph for the 5AhG3 cells.
 

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Probably need to do some more work on the BCM serial data stream.
There maybe flags as yet undiscovered that would reduce regen.

As mentioned faking a low/high temp would def have effects but I can't remember the thresholds.
Use a 'BCM interceptor' equivalent and play with the 2 x temps in the data stream with a pot and see how the MCM reacts.

I would think chopping regen down to about 25% between 0 and -10C would probably do it.
Then stop it completely below -10C if necessary.
 

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Maybe this is mentioned at the beginning of the thread but cars like the Prius, Leaf and some Ford have no heating elements yet these were sold in the Northern tier. If these companies didn't worry why are we?
 

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Discussion Starter · #105 · (Edited)
Maybe this is mentioned at the beginning of the thread but cars like the Prius, Leaf and some Ford have no heating elements yet these were sold in the Northern tier. If these companies didn't worry why are we?
good point. i think it's relevant to what we are learning here.

MY THEORY
"They don't Worry", because if you live in the northern tier and buy a hybrid, you're just an unkowing beta tester for that company, 'guinea pig' It's a tiny market here. 'you' were the one willing to pay 'them' to have your data.

You Could look at the TSB's and the spec adaptations made from 2nd gen compared to the 1st, 3rd to 2nd etc. and figure out what their target market was. the oem's know its a small market so they program around it and learn from those dumb enough to buy into it. If they get lucky and you do all the work to make it work for yourself than they also win.

Inserted Edit here : why does the new tundra hybrid use NiMH? :

on the other hand i can say this, i have lived here my whole life and northern climate folks are huge skeptics of battery powered cars, especially the older folks. not many are willing to risk investing in unproven transportation around here, if it fails you could A. freeze to death or B. waste your money on something stupid that drives you further down the ladder.

if you were willing to drive a hybrid in early 2000's you had to be tough enough to handle the local criticisms that came with the keys. side note, if you could afford a new car, you could afford a heated garage. "those people" were prepared to own hev's. most of 'them' bought a hybrid as a secondary vehicle, they had an ol' reliable that wasn't worth trading in so they hung onto it and tried something new.. something they could fall back on.

i fall into the category of i can't afford gas prices now day's if there's a bin for that. i've never been very tech so im a little behind.. probably never catch up.. but i do my best to stay in the loop. i don't specialize because where i grew up you had to learn how to do everything to stay alive and i like that life.
hev's still have ice's, the car has the ability to run gas only so programmed safeties shouldn't leave you stranded in the cold, built-in back-up :)
if you want it to be warm, drive it in the summer or wear more layers. if you want it to be warmer put a fish house heater next to it. Warmer?.. Fly to Florida ;)
If you don't want dead batteries don't let them freeze or you'll have to be able to afford more batteries. my life is a compromise here. i was taught, life is tough, figure it out
apologies for defending my take on everything as i do realilze it doesn't really relate to the mass majority
 

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I did a test and I was able to trigger the green thermostat and turning on the IMA fan with just cabin heat and 20 seconds of strong wafting with my hand.

I have since installed this short-term solution.

Automotive parking light Hood Automotive tire Automotive lighting Motor vehicle


It's a $10 heater fan that you can buy it right now at the clearance section in harbor freight. I stuck it in the IMA inlet so that it constantly blows some cabin air into the rear speaker area/ green thermostat bay. This seems to work well. There were times without it where the fan would eventually turn off without the battery reaching full temperature. 10° C seems pretty easy with cabin heat. I would still like to insulate the IMA bay.

I tried the heater function and it blew the accessory fuse after a few minutes.


I'd like to switch to a quiet computer fan. Is there a suitable 12v source in the IMA bay that I can pull power from (only when the car is on)?
 

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Discussion Starter · #107 ·
oh my goodness i can't get this out of my head lately.
Disclaimer: you may feel dumber after reading all of this.
okay i propose some more idea's. probably bad ideas but i have to share my thoughts.
first idea... the 12v battery under the hood. why is it under the hood?
i can think of 3 reasons. 1 its under there because it gases off and 2 its close to the starter (shorter, smaller diameter cable) 3 in the event of an accident or roll over the sulferic acid is less likely to burn you.
on other cars ie 2004 buick lesabre's and cadillacs devilles they put the battery under the backseat, with little vent tubes to direct off gasing outside the cabin via grommeted hole through the floor. why did they put it there you might ask? i believe to make it last longer. ask anyone in AZ how long their batteries last.. the heat kills them. under hood temps get hot.. what made me think of this was gasholic's last post with his acc fuse popping heater. that could be remedied if the battery was nearby and or he put proper size wire and proper fuse on that thing. anyways
i think a major design flaw with our little g1's is the "backup starter" the traditional flywheel one on top of the transmission never gets used. my point being, thats not good for it. i was taught if you don't use it you lose it. i know it cranks slower than the ima motor but when your engine oil has the consistancy of molasses at negative temps it would be so much easier on the engine to utilize the little starter to slowly crank the engine over, plus your little starter wouldn't feel so left out. another benfit that would culminate from utilizing the traditional starter is the camshaft snapping.
if you think im kidding i'm not. ive owned my fair share of contractor portable air compressors. the compressor crankshaft typically doubles as the electric motor rotor and when it gets cold enough here they break right in half. the ima starter generates plenty of energy to snap the itty bitty cam the same way. the cam is the weak point because of it's 'built in stress risers', ask a machinist.. anyways honda didn't catch this because this feature was the first of its kind in a car that had to be produced and sold in short order. they weren't going to test it for X amount of cycles, thats what we are for!
so this brings me too,
It would be better for extreme cold people to use traditional starter in winter like those who have already bypassed ima.
relocate the battery to the trunk, vent it to exterior, insulate it with some foam, you need to strap it down so it cant move and properly cover connections so it can't short to chassis ground. additionally you need large gauge cable to reconnect it under hood, if you live in cold you probably have an extra set of big jumper cables you could sacrifice.. at least everybody i know does.. or welding cable or possibly some old car audio cable, or buy a cable long enough.
WHY YOU ASK, i'm trying to get to that part i promise,
the low voltage cranking takes some serious amperage, i don't know how to measure it or calculate it but lead acid batteries can handle dumping the energy very quick without thermal runaway. so anywho the starter gently turns the motor over, what happens next is the real perk.. you basically built your own heat recovery system for the cabin. thats the idea anyways. the battery would warm up even more with bulk charging. the elephant in the room is i have no idea how g1 'thinks'
i know when i went without ima it took several seconds for the backup starter relay to engage so i'm not sure what the qualifiers are, that would be very annoying to wait 5 seconds for take off every time.. beyond that i don't think it would be very easy to delay the bulk charge from the converter until your pack was warm either. i feel there are plenty of pro's and not to many con's but it would take some self motivation and some genious hacking to get it right, if you are without ima its just the command delay...
wow. i took that way too far
if this is a terrible idea, go ahead and shoot me down
 

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Probably need to do some more work on the BCM serial data stream.
There maybe flags as yet undiscovered that would reduce regen.
It would certainly be nice to discover better serial data controls. What we know now can only prevent regen and/or assist entirely. It would be nice to be able to limit regen to specific (non-zero) values, too.

As mentioned faking a low/high temp would def have effects but I can't remember the thresholds.
Use a 'BCM interceptor' equivalent and play with the 2 x temps in the data stream with a pot and see how the MCM reacts.
We can use LiBCM as the 'interceptor'. In fact I've already done this to gather data from an OEM system (with the OEM BCM installed). Instead of a potentiometer, you can just type in whichever value you wish to spoof... if realtime potentiometer adjustment is more desireable, we could hook one up to one of the uncommitted GPIO pins.

I would think chopping regen down to about 25% between 0 and -10C would probably do it.
Then stop it completely below -10C if necessary.
Probably something like that, yeah. We can do this now by dropping the spoofed battery voltage (sent to MCM) down to just above freezing. If we go too low, then the MCM enables background regen, so there's some minimum value we can choose.

...

Maybe this is mentioned at the beginning of the thread but cars like the Prius, Leaf and some Ford have no heating elements yet these were sold in the Northern tier. If these companies didn't worry why are we?
Previously when I considered whether or not to heat the pack, I came to the same conclusion: If Honda doesn't do it, why should we? Even at the beginning of last week I was thinking similarly. However, when the battery drops below freezing cell aging increases rapidly, but we don't know by how much since we don't have the cell chemistry datasheet.

At some point last week I decided we can do better than nothing by adding some form of pack heating. Still TBD if my 5AhG3 solution will actually work well, but if it does then it should greatly extend cell lifetime. Overall, I agree with the basic premise that "if Honda didn't do it, why are we?"

...

It's a $10 heater fan that you can buy it right now at the clearance section in harbor freight. I stuck it in the IMA inlet so that it constantly blows some cabin air into the rear speaker area/ green thermostat bay. This seems to work well.
Yeah all you need to do is get the green temp sensor hot enough to start the IMA fans... once the intake air is warm enough, the fans will stay on. I've definitely got this on my short list of features to add to the firmware, although I'm not certain it's going to happen this week... surprisingly busy doing other things here at the inlaws' house.

There were times without it where the fan would eventually turn off without the battery reaching full temperature. 10° C seems pretty easy with cabin heat. I would still like to insulate the IMA bay.
Observations while driving in Madison:
-If the cabin air isn't appreciably warmer than the battery temp, then when the fans turn on and start sucking in air, that causes the temp sensor to cool down enough that the fans turn off after just a few seconds. This makes perfect sense now that I've seen it, but I certainly didn't think about it as I was writing the "heat pack with fans" logic; I'm more familiar with the "cool pack with fans" environment, wherein cooling the temp sensor off (with fan-driven intake air) is a good thing.
-The pack warms up quite quickly... or at least the temperature sensors do. In FoMoCo they're bolted to the aluminum angles and aluminum battery tray. Probably the battery innards warm/cool slower, but it's pretty difficult to safely place temperature sensors closer to the cells. Note that the OEM sensors (underneath the PCB on each FoMoCo module) aren't safe to use with LiBCM, as they do not meet safety creepage and clearance requirements for the voltage we're operating at.
-Insulating the IMA bay is a great way to minimize heat transfer. However, there's very little room to accomplish this with FoMoCo, and even the 5AhG3 setup probably doesn't offer more than half an inch on the bottom. Keep in mind that you'll want to use non-flammable insulation to minimize collateral fire spread if the cells ever catch on fire. Rockwool is probably the most feasible off-the-shelf insulation for this project. Keep in mind that any insulation you add in the fan air path will reduce the air cooling/heating efficiency. For 5AhG3 this isn't a huge issue; the airflow isn't affected as long as you place all insulation outside the OEM plastic enclosure. However, for FoMoCo pretty much anywhere you place insulation is going to impede air contact with the modules.

I'd like to switch to a quiet computer fan. Is there a suitable 12v source in the IMA bay that I can pull power from (only when the car is on)?
Probably not worth the effort, given that I'll probably change the fan behavior in the next week or so. But to answer your question, yes there's plenty of +12V_IGNITION wires inside the IMA bay.

...

the 12v battery under the hood. why is it under the hood?
i can think of 3 reasons. 1 its under there because it gases off and 2 its close to the starter (shorter, smaller diameter cable) 3 in the event of an accident or roll over the sulfuric acid is less likely to burn you.
IMO, the 12 volt battery is under the hood because that's where the 12 volt battery was most commonly placed in traditional vehicles. As you point out, keeping the cables short decreases starting voltage droop. Also the alternator in a conventional car is located there, too. So basically in a conventional car all the action is up front, so that's where the battery goes. Prior to diving into the engineering design phase, Honda probably reserved the entire rear IMA area for the IMA system, not knowing how much room it would ultimately take up.

Moving the battery into the rear cargo area is certainly possible. The most logical place is probably in the passenger rear cubby behind th IMA bay proper, underneath the small aluminum panel. Leaking and/or venting sulfuric acid probably isn't a significant threat if the battery is sealed. Since the 'alternator' (i.e. the DCDC) is in the rear, you'd only need to run a single cable from the rear-mounted battery positive to the starter solenoid (and also disconnect the OEM positive wire heading from the OEM battery positive terminal to the same solenoid).

For those running LiBCM with a 48S setup, I will eventually add an option to remove the OEM lead acid battery entirely, to be replaced by a lightweight 4S LiFePO4 module. LiBCM already has all the hardware, it's just a matter of making a compatible BMS harness and then writing the firmware. This is a LOW priority feature, so don't expect it anytime soon.

i think a major design flaw with our little g1's is the "backup starter" the traditional flywheel one on top of the transmission never gets used. my point being, thats not good for it. i was taught if you don't use it you lose it. i know it cranks slower than the ima motor but when your engine oil has the consistancy of molasses at negative temps it would be so much easier on the engine to utilize the little starter to slowly crank the engine over, plus your little starter wouldn't feel so left out.

another benfit that would culminate from utilizing the traditional starter is the camshaft snapping.
the cam is the weak point because of it's 'built in stress risers', ask a machinist.. anyways honda didn't catch this because this feature was the first of its kind in a car that had to be produced and sold in short order. they weren't going to test it for X amount of cycles, thats what we are for!
Honestly the IMA crank start is much 'smoother' than the backup starter. The backup starter is undersized and has erratic brushed torque, which imparts massive jerk (i.e. the derivative of acceleration) onto the crankshaft. This causes chatter on the entire system. The 'chugging' you experience with a traditional starter imparts way more wear on the linkages than you might think... it's not the "slowly crank" scenario you describe, but rather a taxing herk and jerk until the engine combustion cycle takes over.

In contrast, the IMA motor is massively oversized, has a smooth torque ramp-up profile, and doesn't have all that cranking chatter. The smooth ramping profile minimizes 'chugging' which reduces wear and tear on the various internals. My guess is an IMA start is several times less bad for the engine, as compared to the backup starter.

I do agree that by failing to routinely test the backup starter (e.g. 1 in 100 starts), the starting system could degrade without the user knowing about it until the IMA system fails (e.g. poor ground straps, weak 12 volt battery, etc). So yes, I agree Honda should have added a periodic backup starter test routine... although that might have been confusing to the customer.

It would be better for extreme cold people to use traditional starter in winter like those who have already bypassed ima.
FYI: The only reason Honda uses the backup starter in cold weather is to prevent damaging the NiMH cells.

relocate the battery to the trunk, vent it to exterior, insulate it with some foam, you need to strap it down so it cant move and properly cover connections so it can't short to chassis ground. additionally you need large gauge cable to reconnect it under hood,
I agree with this, except maybe just buy a sealed lead acid battery instead of venting.

the low voltage cranking takes some serious amperage, i don't know how to measure it or calculate it
To measure you'd add maybe a 1 mOhm resistor in series with the positive start lead, then connect an isolated differential oscilloscope probe to both ends.

what happens next is the real perk.. you basically built your own heat recovery system for the cabin. thats the idea anyways. the battery would warm up even more with bulk charging. the elephant in the room is i have no idea how g1 'thinks'
We 100% understand how the "g1 'thinks'" about the 12 volt battery, so that's not an issue. However, the 12 volt battery isn't going to reliably/appreciably/controllably heat the IMA bay. There's just too many variables to consider, most notably that you'll damage the 12 volt battery if it's already full and you keep charging it until it heats up. The same principals apply to heat generated by the DCDC converter... if the battery is already full, then there's nowhere for the DCDC to output its power too, hence it's not going to appreciably heat up.

Joule heating via discrete resistors is a much better solution, plus we won't damage anything if we power them constantly overnight (assuming they're designed properly).

i know when i went without ima it took several seconds for the backup starter relay to engage so i'm not sure what the qualifiers are, that would be very annoying to wait 5 seconds for take off every time..
You can enable immediate backup starter by shorting out the "bypass starter relay". I described this modification several times here on ic and several members have successfully implemented it. Note that you can also disable the 5 second delay by spoofing a few signals on the MCM control wires that head back to the ECM.

beyond that i don't think it would be very easy to delay the bulk charge from the converter until your pack was warm either. i feel there are plenty of pro's and not to many con's but it would take some self motivation and some genious hacking to get it right, if you are without ima its just the command delay...
All the 'genius hacking' has already occurred... it's not actually that difficult to implement the features you've proposed. However, it doesn't achieve the goal you envision... resistance heating is a much better solution.
 

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Discussion Starter · #109 ·
I rocked a t-shirt part of the day yesterday! and 37F again today.
thanks @mudder for clarifying my several thoughts.
i know your on the path of "the most logical solution"
the more i thought after i posted, the more i realized its a really bad idea. it would only add more mass to the problem area.
im going to keep bouncing ideas until mudder draws the line in the snow
is there any way to rob heat off of the igbt heat sink?? i watched your youtube where you dissected one on the bench..
it looks like it gets hot, but may require to much trickery to get it to produce heat during a cold start if engine is unloaded and idling..
 

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is there any way to rob heat off of the igbt heat sink?? i watched your youtube where you dissected one on the bench..
it looks like it gets hot, but may require to much trickery to get it to produce heat during a cold start if engine is unloaded and idling..
We've certainly discussed sinking heat from/to the IGBT ducting system when the car is in use. One of the primary difficulties is we don't want to expose the dirty exterior air to the IMA bay. Another issue is we can only generate heat in the IGBT by rotating the motor, so once again we're at the mercy of whether or not the motor is spinning.
 

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We can use LiBCM as the 'interceptor'. In fact I've already done this to gather data from an OEM system (with the OEM BCM installed).
Remember that the different BCMs and MCMs will act differently so you will want to put your tests into code rather than do them manually so you can reproduce them on different versions.

I have a small collection of BCMs and MCMs and enough connectors and slow and fast Ardiunos and ADCs and DACs and RS-485 modules and FETs and some spare Pis dying to run Python scripts (and even an Arduino 4000 Vidor with an FPGA that I need to learn more about) and characterizing these is something I have wanted to do for a long time. So if you get something started, I will almost certainly want to duplicate it and add test cases to hit a variety of MCMs and BCMs with.
 

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1) Insulate. It's difficult in the IMA area and the car being aluminium conducts heat very well to the outside.
Too much permanent insulation might easily cause overheating in the summer/hot climates.

2) Introducing heat is difficult and it will leak away very fast unless the IMA is insulated.

I prefer the simple fan solutions so far.

Maybe flip the OEM battery fan around and put a simple heater element on it designed for 120mm fans.

Or use a reversible 120mm fan.

Or have a fan sandwich. OEM SUCK FAN - HEATER ELEMENT - NEW BLOW FAN

Stego. HVL031 The do 100-400w versions at various voltages 120/220 etc
Simple resistive element control with DC pwm or AC triac etc

Gas Home appliance Font Machine Computer component





I suspect there is enough room inside the oem fan shroud/duct to mount an element inside it.

Or simple wire element ones designed for 120mm fans.


There are zillions of cheap ceramic heating elements around..
 

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sit down with a cup of tea and enjoy my perspective.

put a toaster in your deepfreezer on side A, put a hair dryer aimed at slice of bread on side B.
now have a toast RACE!
mudder made an awesome youtube on how inefficient the fan thing is and he was in a warm garage. he's right.
i believe any forced air solution will take a lot more energy than you can imagine.
i know what he's talking about, a couple weeks ago i was on a job where i installed 30 4'x6' windows into a addition space that wasnt heated yet, the indoor temp and outdoor temp was around 5F. the new window's needed to have spray foam insulation applied between the framing. i prepared by setting my warm cans of sprayfoam in the homeowners 70F cabin the night before.

i spent over 10 minutes trying to get the foam to come out of the first can using my foam gun.. i started spraying at "normal speed" however within the first minute the foam started coming out slower and slower until it was just trickling out and my hands started freezing so i got upset that i wasn't winning and the clock was ticking. i wen't inside to fetch a hot pale of water so i could rotate my cans in hot water.. and i hadn't realized that the homeowners had there pipe's drained for the winter as this place was only their summer cabin, no hot water, strike two.

Thats when i remembered i had an old hairdryer in my trunk! I Had to heat my cans of insulation every five minutes in 5F environment. i also learned that the cfm in the hairdryer was designed to pull in warm air, at first the blow dryer wasn't even working.. i had to cup my hand over the inlet to restrict the cfm going through the coils to get the increase in air temperature that i needed to come out the exhaust side.

I was able to get one can up to a "working temperature". this allowed me to get a 5 minute window of working time, i repeated this process until all the windows were insulated around the perimeters.. taking over twice as long as i had planned because of my poor assumption that starting with a 70F can would've been enough.

Forced air will draw a lot of juice to run a fan. the fan will only speed up the heating of air that is farther away and insulating the cabin is out of the question. I believe when heating the batteries you only want to heat localized near the battery for effiicency and insulate the heck out of the ima bay. mudder has the best 'add-on solution' for 5ahG3 people, it will be more efficient if we could completly air-seal the ima bay.

You can't forget, if you can get the cabin up to 70F and it's cold outside, opening the door to get in or out of the car basically loses all the energy you just saved. worse than stepping out into arctic temps, you than have to open the rear hatch to grab your tools for the day out or groceries. whenever winter 'decides to get here' maybe i will demonstrate a video of how fast the cabin temp drops via video and i promise you won't want to live here.

it defies your interpretation of physics. i compare the cold here to stuff thats really hot. pick an ideal temperature of 70F.. you can pick up a 70F bowling ball no problem. now add 100 degrees to that. can you pick up a 170 degree bowling ball. no. it burns your hands. okay lets go the other direction. try picking up a -30F bowling ball. it also burns your hands. im a bowler, i have forgotten my ball in the truck for a week before, you bring it in the warm alley and it sweats condensation out of it for 2 HOURS and you bowl bad scores because it doesn't hook or react with the behavior you learned when it was always 70F. i know rent a heated locker in the bowling alley.

we know the ideal temperature for different batteries: we should be aiming for that target, not the low side or the high side, the target. best mpg comes from conservation of momentum/energy. acceleration and deceleration kills mpg.

now do that with your battery temperature and it will extend the life of the battery.
I might figure out that if outside temp dips to a certain point that the car will be undriveable without an efficient supplemental solution. I will be forced to leave the lithium plugged in and call for a ride. The entire cabin is a heatsink at the the speed limit, 60mph air that is well below zero sucks all the heat out faster than you can make it at some point. this is why i think about sprayfoaming the underside of the battery area on the exterior of the car.

I already know that cold temps throw the oem battery management system out of whack. my soc was stable all summer and it does wacky roller coaster stuff now because of false readings on temp sensors. If i'm wrong, where's the thread?.. i'll read it.

mainting heat would be ideal for long periods of cold exposure. On -30F days it takes most four cylinder cars a half hour of driving with load to get the cabin air warm and the foam in your passenger seat is still stiff as a board. If you drive a diesel you don't shut it off, period, you have to plug in block heater over night blanket the radiator, you have to add an extra battery for cranking, sometimes supplement that with 100 amps from a battery booster, tand put isoheet in your fuel. lines gel up and your done, game over, tow it into a warm building.
thats enough thinking for now, it's nice outside and i have chores to tend
 

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Discussion Starter · #115 ·
1) Insulate. It's difficult in the IMA area and the car being aluminium conducts heat very well to the outside.
I agree, imagine parking your car in a freezer with the wind blowing.. it pulls the heat out like its a heat sink.
Too much permanent insulation might easily cause overheating in the summer/hot climates.
i agree, if your willing to drive a hybrid in extreme conditions you need to be able to adapt to hot or cold.
 

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Thanks Mudder! A few questions:

Your first solution was going to require the fast charger. Should this current approach work with the stock charger and RevC PCB?

Also was the pre-release firmware that caused you problems 0.8.4g? Just checking, as I'm planning to load that tomorrow.

-Bryan
 

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Dumb idea???
I didn't read the entire thread. Maybe this has been discussed already? Similar to Mudder's approach to keep lithium batteries from freezing.

$7 (plug-in) battery heater:
A pair of 400 ohm 100watt wire wound resistors wired in parallel and bolted to opposite ends of the aluminum IMA battery surround/housing (acting as a heat sink or heat radiator). Electricity supplied via (fused) external 120vac:

120vac / 200ohm = 0.6amps = 72 watt battery compartment space heater
Could be set on a timer or plugged in as needed.

 

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Your first solution was going to require the fast charger. Should this current approach work with the stock charger and RevC PCB?
This will depend on how much power is ultimately required to keep the modules warm. If it's less than 85 watts, then yes, the stock charger and RevC PCB will work just fine.

Also was the pre-release firmware that caused you problems 0.8.4g? Just checking, as I'm planning to load that tomorrow.
Yes, the issue was with v0.8.4g, but I believe it only applies to 60S.
 

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A pair of 400 ohm 100watt wire wound resistors wired in parallel and bolted to opposite ends of the aluminum IMA battery surround/housing (acting as a heat sink or heat radiator). Electricity supplied via (fused) external 120vac:
Yes, this is an idea on the table for 47 Ah FoMoCo. Note that we'll need to derate that type of resistor substantially; running them at 100% causes too much of a heat gradient. If we go that route, then we'll probably need something like 500 watts nameplate rating to deliver 100 watts. Otherwise they get too hot. For example, I'm sinking at most 75 watts into a "250 watt" resistor and it's heating up to 110 degC.
 
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